In today's world, many real-life processes are either improved by new sophisticated ICT technologies or altered. Collaboration, as a respected method in learning, is such a process. Lately there is ongoing research and a lot of innovations in the area of collaborative learning. In this paper we present a new model of on-line collaborative activity for building ontology. It enriches the list of activities that can be included in the course curriculum, and also, at the end, produces ontology for course domain. We realize an experiment and compare the results obtained by a set of students in this activity with the final course results. The conclusions show that there is a significant correlation between them. Therefore, we recommend this model as a very good activity for collaborative ontology building in the e-learning processes.